The fushi tarazu (ftz) gene of Drosophila melanogaster functions in determining the formation of alternating segmental primordia during the early stages of embryogenesis. Ftz mutations affect the expression of engrailed (en), a gene required for the determination of posterior segment primordia, and Antennapedia (Antp) a gene required for determining the identity of thoracic segmental primordia. The objective of this proposal is to test the hypothesis that the homeodomain-containing protein encoded by ftz activates the transcription of en and Antp by binding to specific DNA sequences near these genes. ftz protein binding sites will be identified by DNase I footprinting using a beta- galactosidase-ftz fusion protein purified from E. coli extracts. How the deletion of ftz binding sites affects en and Antp expression will be assessed in vivo in embryos that contain transformed copies of en-lac Z or Antp-lac Z reporter gene fusions. The mechanism of ftz regulation will be probed by experimenting with the number, location and orientation of ftz binding sites at the en and Antp loci in lac Z reporter gene fusions. Results from these experiments will help explain how spatial patterns of gene expression in embryos are generated through genetic regulatory mechanisms and will provide an example of how homeodomain-containing proteins regulate gene expression.